Chabertia ovina, the large-mouthed bowel worm is a species of parasitic roundworms that infects sheep, goats (occasionally cattle) and other wild ruminants. Infection of pigs are very infrequent.
It is found worldwide but is more frequent in regions with a temperate climate. In a study in Sweden 80% of the sheep flocks investigated were infected with Chabertia ovina, and the highest incidence found in a flock was 56%. Studies in flocks in southern Germany showed 98% of the sheep flocks and 84% of the goat flocks to be infected.
These worms do not affect dogs and cats.
The disease caused by Chabertia worms is called chabertiasis or chabertiosis.
Is livestock infected with Chabertia ovina contagious for humans?
- NO: The reason is that these worms are not human parasites.
Final location of Chabertia ovina
Predilection site of adult Chabertia ovina is the large intestine.
Anatomy of Chabertia ovina
Chabertia ovina adults are 1 to 2 cm long, whereby females are larger than males.
As in other roundworms, the body of Chabertia ovina worms is covered with a cuticle, which is flexible but rather tough. The worms have a tubular digestive system with two openings. Characteristic for these worms is a large cup-shaped mouth capsule, without teeth.
They also have a nervous system but no excretory organs and no circulatory system, i.e. neither a heart nor blood vessels.
Males have a rather large copulatory bursa with two long and thin spicules for attaching to the female during copulation.
The eggs are ovoid, about 50x90 micrometers, have a thin shell and contain more than 16 cells (Blastomeres).
Chabertia ovina has a direct life cycle, i.e. there are no intermediate hosts involved. Adult females lay eggs in the large intestine of the host that are shed with the feces. Once in the environment the eggs release the L1-larvae that complete development to infective L3-larvae in about 7 days. This development can also take place by rather low temperatures (~5°C). By moist weather these larvae can survive on pasture and remain infective for up to 10 months.
Livestock becomes infected after ingesting infective larvae with pasture, but also indoors with contaminated hay. Immature larvae attach to the wall of the small intestine and feed voraciously on the tissues. About a week later they detach and migrate to the cecum, where they complete development to adult worms, which move to the colon, their predilection site. There they attach to the wall with their mouth capsule and females start laying eggs (up to 10'000 eggs daily!). L4 larvae can become arrested (dormant, hypobiotic) in the tissues to survive the cold or the dry season.
The prepatent period (time between infection and first eggs shed, without dormancy) is about 7 weeks.
Harm caused by Chabertia ovina, symptoms and diagnosis
In most regions Chabertia ovina is not the most harmful among the gastrointestinal worms that affect sheep and goats, but worsens the damage caused by other species (e.g. Haemonchus spp, Ostertagia spp, etc.). Adults and larvae do not suck blood but may ingest some if a blood vessel is damaged. Nevertheless they harm the gut's lining where they attach, whereby they often change their attachment site multiplying the lesions.
These causes small but numerous local ulcers, sometimes also bleeding, which can be significant in case of massive infections. Seriously affected animals can show diarrhea (mucous or hemorrhagic), anemia, weight loss, and can even die. In less severe cases they may lose weight and produce less wool.
Chabertia ovina does not seem to be pathogenic for cattle.
Since most infections are mixed with other gastrointestinal roundworms (e.g. Haemonchus spp, Ostertagia spp, Trichostrongylus spp, etc.) it is often difficult to ascribe the damage to Chabertia sppor to other worms.
Diagnosis is based on the clinical signs and confirmed after detection of characteristic eggs in the feces. To differentiate thes eggs from those of Oesophagostomum L3 larvae have to be cultivated from the eggs.
Prevention and control of Chabertia
Being quite resistant to adverse environmental conditions, Chabertia larvae can survive up to 10 months on pasture, which makes it quite difficult to reduce the populations. Or they spend the winter as dormant larvae. This ensures re-infection of the pastures during the next spring.
As a general rule, whatever reduces pasture contamination with infective larvae (e.g. adequate pasture rotation) or exposure of livestock to such larvae will diminish the impact on the herd. Such preventative measures are the same for all gastrointestinal roundworms and are explained in a specific article in this site (click here).
Livestock exposed to these worms often develop natural resistance progressively and may recover spontaneously. Such resistant animals do not become sick if re-infected, but continue shedding eggs that contaminate their environment.
Numerous broad spectrum anthelmintics are effective against adult worms and larvae, e.g. several benzimidazoles (albendazole, febantel, fenbendazole, oxfendazole, etc.), levamisole, as well as several macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin). But not all of them are effective against arrested larvae of Chabertia ovina. Read the product label carefully to find it out.
Depending on the country most of these anthelmintics are available for oral administration as drenches, feed additives and/or tablets. Levamisole and most macrocyclic lactones are usually also available as injectables. A few active ingredients are also available for livestock as pour-ons and slow-release boluses.
In numerous countries monepantel, an anthelmintic of a new chemical class, is also available as a drench sheep. It is effective against Chabertia ovina adults and immature L4 larvae, but not against inhibited larvae. It is not approved for cattle.
Numerous commercial products contain mixtures of two or even more active ingredients of different chemical classes. This is done to increase the chance that at least one active ingredient is effective against gastrointestinal worms that have become resistant, or to delay resistance development by those worms that are still susceptible.
Excepting slow-release boluses, most wormers containing benzimidazoles (e.g. albendazole, febantel, fenbendazole, oxfendazole, etc.), levamisole, tetrahydropyrimidines (e.g. morantel, pyrantel) and other classic anthelmintics kill the worms shortly after treatment and are quickly metabolized and/or excreted within a few hours or days. This means that they have a short residual effect, or no residual effect at all. As a consequence treated animals are cured from worms but do not remain protected against new infections. To ensure that they remain worm-free the animals have to be dewormed periodically, depending on the local epidemiological, ecological and climatic conditions. An exception to this are macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin), that offer several weeks protection against re-infestation, depending on the delivery form and the specific parasite.
There are so far no true vaccines against Chabertia ovina. To learn more about vaccines against parasites of livestock and pets click here.
Biological control of Chabertia ovina (i.e. using its natural enemies) is so far not feasible. Learn more about biological control of worms.
You may be interested in an article in this site on medicinal plants against external and internal parasites.
Resistance of Chabertia ovina to anthelmintics
Resistance of Chabertia ovina to the most used anthelmintics (benzimidazoles, ivermectin, levamisole, etc) in sheep and goats does not seem to be a problem as it is for other gastrointestinal roundworms (e.g. Cooperia spp, Haemonchus spp, Ostertagia spp, Trichostrongylus spp, etc.).
This means that if an anthelmintic fails to achieve the expected efficacy against Chabertia ovina, there is a lcertain risk that it is due to anthelmintic resistance. But it is well known that many cases of product failure are due to incorrect use of a product, or to the use of an unsuited product, not to resistance.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Chabertia control.